Vitamin B12, otherwise known as cobalamin, is the largest and most structurally complex of the eight water-soluble B vitamins. Vitamin B12 is a class of cobalt and corrin ring molecules that possess vitamin activity. The sixth coordination site of the corrin ring is either a cyano group (—CN), a hydroxyl group (—OH), a methyl group (—CH3) or a 5′-deoxyadenosyl group, creating four forms of vitamin B12, including, cyanocobalamin, hydroxocobalamin, methylcobalamin, and adenosylcobalamin.
Vitamin B12 is synthesized by microbes, but not by humans or plants. Gastrointestinal absorption of vitamin B12, from food or supplements, depends on the presence of sufficient intrinsic factor and calcium ions. Adenosylcobalamin and methylcobalamin are the active forms of vitamin B12 in humans. Vitamin B12 deficiency may result from intrinsic factor deficiency (pernicious anemia), partial or total gastrectomy, or diseases of the distal ileum, intestinal problems and nerve damage, etc. Conditions that make people vulnerable to vitamin B12 deficiency include: Crohn's disease, multiple sclerosis, HIV/AIDS, advanced age (>65 years), chronic intestinal inflammation, intestinal surgery, food moving too quickly through the intestine, strict vegetarian diets, excessive alcohol consumption for longer than 2 weeks, long-term use of acid reducing drugs, or drug-therapy associated with anemia.
Vitamin B12 has also been used in the treatment of IgE-mediated allergic diseases, such as allergic rhinitis and asthma. Oral ingested vitamin B12 is ineffective in the treatment of allergic disease, possibly due to liver metabolism.
Cyanocobalamin (Crystamine, Cyomin, Crysti 1000, Nascobal®) is the most widely sold analogue of vitamin B12. Cyanocobalamin is available in injectable (subcutaneous or intramuscular) and oral forms and has the advantage of having a stable shelf life at standard temperature and pressure (STP). Nascobal®, an intranasal gel formulation of cyanocobalamin, has been clinically shown to maintain adequate serum levels of vitamin B12. The nasal gel can be self-administered through a nasal delivery system that avoids the discomfort of intramuscular injections of B12.
Since vitamin B12 is very large, orally ingested cyanocobalamin is improperly digested and only small amounts of the vitamin get absorbed by the host. The drawback of the injectable form is that it is invasive, expensive, and inconvenient. Hence, there is a need for more effective forms of vitamin B12 that can be absorbed more easily to ameliorate conditions associated with vitamin B12 deficiency.